Photographic objective.



35o-47o SR 1 E' G. S. DEY & M. ZWILLINGER. PHOTOGRAPIIIG OBJECTIVE. APPLICATION FILED JULY 3l. |915. 1,1 60,148. Patented Nov. 16, 1915.

WTNESSES. Lcfs K M MM5 'al' CDLUIIIA mi" D I UNITED sTATEs PATENT oEEIoE.

GILBERT S. DEY AND MAX ZWILLINGER, 0F ROCHESTER, NEW YORK, ASSIGNORS TO EASTMAN KODAK COMPANY, 0F ROCHESTER, NEW YORK, A CORPORATION 0F NEW YORK.

PHOTOGRAPHIC OBJECTIVE.

Application led July 31, 1915.

T 0 all whom t may concern.'

Be it known that we, GILBERT S. DEY and MAX ZWILLINGER, of Rochester, in the county of Monroe and State of New York, have invented certain new and useful Improvements in Photographic Objectives; and we do hereby declare the following to be a full, clear, and exact description of the same, reference being had to the accompanying drawings, forming a part of this specification, and to the referencenumerals marked thereon.

Our present invention relates to optics and more particular to the construction of photographic objectives and it has for its object to produce a compound lens for this purpose corrected for chromatic and spherical aberration, distortion, astigmatism and curvature of field and in which the number of different radii to which the several lens surfaces are ground will be reduced to a minimum, thus materially reducing the costr of production through simplifying the mechanical processes of manufacture.

A further object of the invention is to produce a lens system from symmetrically formed units so that the possibility of making mistakes in placing them in the mounting is materially reduced if not obviated and the cost of assembling thereby lowered.

To these and other ends the invention resides in certain improvements and combinations of parts all as will be hereinafter more fully described, the novel features being pointed out in the claims at the end of the specification.

In the drawing the figure is a diagrammatic view of a lens system constructed in accordance with and illustrating one embodiment of our invention.

The combination or system of our invention consists of four simple lenses separated by air spaces. Referring to the drawing, the irst and fourth marked 1 and 4 respectively, at the two ends are positive or collective lenses. They are of the same form, equal and symmetrically placed as to the center of the combination but the opposite faces of each lens are ground to diderent radii. Hence but two radii are involved in the grinding of both lenses. The second and third simple lenses, marked 2 and 3 are negative or dispersive lenses. They are equal and symmetrical in form, all four faces thereof being ground to the same ra- Speccaton of Letters Patent.

Patented Nov. 16, 1915.

Serial No. 42,982.

dius so that only one radius is involved in the grinding of both of these. There are therefore only three radii involved in the whole system.

Theoretically the problem has been to find an anastigmatic combination with flat curves, based on the fundamental condition that IszRzR--RG (see drawing), or in other words that the two negative lenses should be equal and symmetrical in form, and the condition that R1=R8 and R2=R,. These conditions added to the usual conditions in lens theory led to the derivation of the relative dispersion of the glasses, the relative powers of the lenses, their refractive indices, spacings, thicknesses, and finally the radii of the lenses. The data given below shows the final solution for an aperture of one eighth the focal length, in which zero astigmatism occurs at 23 from the optical axis, and the maximum astigmatic difference inside this point occurs at 18 and is less than one per cent. of the focal length.

Table of elements corresponding to equivalent focal In this table (l), (2), (3), (4:) represent the lenses in order, as shown in the drawing. G is the index of refraction of the glass for the G line of the spectrum; D is the index for the D line; R1, R2 represent the radii of the lens surfaces in order, as shown in the drawing; T1, T2 represent the thicknesses of the lenses; and S1, S2, S3 the air spaces between the lenses.

While showing one form of the lens in the above table, we obviously do not consider our invention limited to the eXact details thereof as, for instance, the thicknesses and separations should be considered as non-essentials as also the glass indices and the numerical values of the radii. The essential condition in the above embodiment is that R1=R8; R2=R7 R3=R4 :R5-:R6 and because of this, fewer tools are required in grinding this lens than with other four lens combinations and the symmetry of the units eliminates the possibility of making mistakes in placing them in the mount.

Ve claim as our invention:

l. A photographic objective consisting of four elements, two of which are equal positive lenses, symmetrically placed in the combination but unsymmetrical in form, and the other two of which are equal and symmetrical negative lenses, the eight lens surfaces being ground to three common radii.

2. A photographic objective corrected Jfor spherical aberration, chromatic aberration and astigmatism consisting of four simple lenses, two of which are equal positive lenses symmetrically placed in the combination but unsymmetrical in form and two equal and symmetrical negative lenses, the four surfaces' of the latter being ground to one radius and the opposite surfaces of each of the positive lenses being ground to two different radii which two radii are the same in each lens.

GILBERT S. DEY. MAX ZWILLINGER.

lVt'ness: l

JOSEPH Q. ONEILL.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,- Washington, D. C. 

